This research is producing digital cartographic models of the urban space of Rome, NY. Workingbetween two software packages for spatial visualization that are now ubiquitous in architecture (FormZ)and geography (ArcView), the project takes an interdisciplinary approach to understanding howavailable data sources and modes of visualization enable ...

This research is producing digital cartographic models of the urban space of Rome, NY. Workingbetween two software packages for spatial visualization that are now ubiquitous in architecture (FormZ)and geography (ArcView), the project takes an interdisciplinary approach to understanding howavailable data sources and modes of visualization enable or discourage particular understandings ofurban space. The project is designed specifically to work within, and develop, a critique of theconstraints of the two software packages. Rather than encouraging a deceptively smooth integration ofwhat may be fundamentally incommensurable forms of knowledge, this project begins with the premisethat vocabularies and conceptions of space vary considerably in various disciplines, as do the modes ofvisualization that each has developed to represent, document, examine, and produce space. Minimize

Supernova experiments to characterize dark energy require a well designed low redshift program; we consider this for both ongoing/near term (e.g. Supernova Legacy Survey) and comprehensive future (e.g., SNAP) experiments. The derived criteria are: a supernova sample centered near z=0.05 comprising 150-500 (in the former case) and 300-900 (in the...

Supernova experiments to characterize dark energy require a well designed low redshift program; we consider this for both ongoing/near term (e.g. Supernova Legacy Survey) and comprehensive future (e.g., SNAP) experiments. The derived criteria are: a supernova sample centered near z=0.05 comprising 150-500 (in the former case) and 300-900 (in the latter case) well measured supernovae. Low redshift Type Ia supernovae play two important roles for cosmological use of the supernova distance-redshift relation: as an anchor for the Hubble diagram and as an indicator of possible systematics. An innate degeneracy in cosmological distances implies that 300 nearby supernovae nearly saturate their cosmological leverage for the first use, and their optimum central redshift is z=0.05. This conclusion is strengthened upon including velocity flow and magnitude offset systematics. Limiting cosmological parameter bias due to supernova population drift (evolution) systematics plausibly increases the requirement for the second use to less than about 900 supernovae. Minimize

A scenario is explored in which Lyα absorbers at low redshift arise from lines of sight through extended galaxy disks, including those of dwarf and low surface brightness galaxies. A population of galaxies is simulated based upon observed distributions of galaxy properties, and the gas disks are modeled using pressure and gravity confinement. So...

A scenario is explored in which Lyα absorbers at low redshift arise from lines of sight through extended galaxy disks, including those of dwarf and low surface brightness galaxies. A population of galaxies is simulated based upon observed distributions of galaxy properties, and the gas disks are modeled using pressure and gravity confinement. Some parameter values are ruled out by comparing simulation results with the observed galaxy luminosity function, and constraints may be made on the absorbing cross sections of galaxies. Simulation results indicate that it is difficult to match absorbers with particular galaxies observationally since absorption typically occurs at high impact parameters (> 200 kpc) from luminous galaxies. Low impact parameter absorption is dominated by low luminosity dwarfs. A large fraction of absorption lines is found to originate from low surface brightness galaxies, so that the absorbing galaxy is likely to be misidentified. Low redshift Lyα absorber counts can easily be explained by moderately extended galaxy disks when low surface brightness galaxies are included, and it is easily possible to find a scenario which is consistent with observed the galaxy luminosity function, with low redshift Lyman limit absorber counts, and with standard nucleosynthesis predictions of the baryon density, ΩB. Subject headings: galaxies: fundamental parameters, luminosity function— intergalactic medium — quasars: absorption lines 1 Linder Comparing Galaxies and Lyα Absorbers 2 1. Minimize

orrelation between impact parameter and column density can occur largely as a result of selection effects. The nearest galaxy is likely to be observed at an impact parameter around a few hundred kpc whether it gives rise to absorption or not, unless a strong absorption line is seen. Thus while it is clear that at least some stronger (? 10 16 cm ...

orrelation between impact parameter and column density can occur largely as a result of selection effects. The nearest galaxy is likely to be observed at an impact parameter around a few hundred kpc whether it gives rise to absorption or not, unless a strong absorption line is seen. Thus while it is clear that at least some stronger (? 10 16 cm \Gamma2 ) absorption lines arise in galaxies, making such plots does not allow for a meaningful test of the relationship between galaxies and weaker absorbers. While there is no reason to think that gas around galaxies should be cut off at any particular column density, other tests, such as those in which the absorption cross sections of galaxies are examined for a wide range of galaxy properties, will be needed to establish the relationship between absorbers and galaxies. References Minimize

Abstract. I explore the hypothesis that Lyα absorption at low redshift is caused by the outer regions of extended galaxy disks, including those of dwarf and low surface brightness galaxies. McGaugh (1996) has shown that the distribution of central galaxy surface brightnesses may be flat to 25 B mag arcsec −2 or fainter. A population of galaxies ...

Abstract. I explore the hypothesis that Lyα absorption at low redshift is caused by the outer regions of extended galaxy disks, including those of dwarf and low surface brightness galaxies. McGaugh (1996) has shown that the distribution of central galaxy surface brightnesses may be flat to 25 B mag arcsec −2 or fainter. A population of galaxies is simulated based upon observed distributions. The low-redshift neutral column density distribution is predicted, and an estimate is made for the number density of disk galaxies required to explain all absorbers. Results relating to galaxy luminosities and impact parameters are discussed. Determining the relation between galaxies and Lyα forest absorbers is complicated by uncertainties in the extent and configuration of galactic gas as well as uncertainties in the properties of the galaxy population. The possibility is explored that forest absorbers at low redshift can be explained by highly extended, outer galaxy disks, where galaxies obey a flat central surface brightness distribution. This model is likely to represent field galaxies best, as interactions and Minimize

. Understanding galaxy evolution will require knowledge of the properties of the low redshift galaxy population. Many nearby galaxies are difficult to detect in optical surveys because they are low in surface brightness. Furthermore, the gaseous extent of galaxies has not been well constrained due to the possible presence of ionized gas beyond w...

. Understanding galaxy evolution will require knowledge of the properties of the low redshift galaxy population. Many nearby galaxies are difficult to detect in optical surveys because they are low in surface brightness. Furthermore, the gaseous extent of galaxies has not been well constrained due to the possible presence of ionized gas beyond where galaxy disks are seen to cut off in 21 cm maps. UV observations of Lyff absorption along quasar lines of sight therefore allow for an especially powerful probe of gas in galaxies. I show that it is possible to simulate a population of galaxies at low redshift which is consistent with galaxy observations, explains low redshift Lyff absorber counts, and is consistent with the baryon density as predicted by standard big bang nucleosynthesis. By comparing simulation results with observed galaxy luminosity functions, an upper limit can be found for the characteristic absorbing cross section of galaxies. INTRODUCTION Absorption line. Minimize

The effects of galaxy selection on our ability to constrain the nature of weak Lyα absorbers at low redshift are explored. Current observations indicate the existence of a substantial population of gas-rich, low surface brightness (LSB) galaxies, and these galaxies may have large cross sections for Lyα absorption. Absorption arising in LSB galax...

The effects of galaxy selection on our ability to constrain the nature of weak Lyα absorbers at low redshift are explored. Current observations indicate the existence of a substantial population of gas-rich, low surface brightness (LSB) galaxies, and these galaxies may have large cross sections for Lyα absorption. Absorption arising in LSB galaxies is likely to be attributed to high surface brightness galaxies at larger impact parameters from quasar lines of sight, so that the observed absorption cross sections of galaxies may seem unreasonably large. Thus it is not currently possible to rule out scenarios where LSB galaxies make substantial contributions to Lyα absorption using direct observations. Less direct tests, where observational selection effects are taken into account using simulations, should make it possible to determine the nature of Lyα absorbers by observing a sample of ∼ 100 galaxies around quasar lines of sight with welldefined selection criteria. Such tests, which involve comparing simulated and observed plots of the unidentified absorber fractions and absorbing galaxy fractions versus impact parameter, can distinguish between scenarios where absorbers arise in particular galaxies and those where absorbers arise in gas that traces the large scale galaxy distribution. Care must be taken to minimize observational selection effects even when using these tests. Results from such tests are likely to be dependent upon the limiting absorption line equivalent width or neutral hydrogen column density. While not enough data are currently available to make a strong conclusion about the nature of moderately weak absorbers, some evidence is seen that such absorbers arise in gas that is around or between galaxies that are often not detected in surveys. Subject headings: galaxies: fundamental parameters — intergalactic medium — quasars: absorption lines — large-scale structure of universe Minimize